Do I need underlayment under shingles?

Yes. Underlayment is required by most codes and all shingle manufacturer warranties. It is your secondary moisture barrier if shingles are damaged.

Felt vs. synthetic underlayment — which should I use?

Synthetic underlayment is now preferred by most roofers. It is lighter, tear-resistant, walkable, and can be left exposed longer. Felt can absorb moisture and tear during installation.

Roofing Underlayment Calculator

Calculate how many rolls of roofing felt or synthetic underlayment you need.

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Enter Your Measurements

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How to Use This Calculator

1Enter total roof area.
2Select the underlayment type you are using.
3Click Calculate.

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About This Material

Roofing underlayment is the moisture barrier installed over the roof sheathing before shingles. Options: 15# felt (economical, 400 sq ft/roll), 30# felt (heavier, 200 sq ft/roll), synthetic (lighter, stronger, 1000 sq ft/roll).

Installation Tips

•Install horizontally, starting at the eave.
•Overlap each course 2–4 inches over the one below.
•Use ice and water shield in the first 2 courses in cold climates.
•Fasten with cap nails or staples per manufacturer instructions.

Common Mistakes to Avoid

Installing in the wrong direction (should go horizontal).
Not using ice and water shield near eaves — required in climate zones with freezing.
Using staples in high-wind areas instead of cap nails.